Coreactive photoinitators

ABSTRACT

Compounds of the formula 
     
         RG--A--IN 
    
     wherein 
     IN is a photoinitiator basic structure 
     A is a spacer group and 
     RG is a functional reactive group 
     can be employed as coreactive photoinitiators for photopolymerization of systems containing ethylenically unsaturated compounds.

This is a continuation of Ser. No.07/951,299, filed Sep. 24, 1992, nowabandoned, which is a continuation of Ser. No.07/720,141, filed Jun. 24,1991, now abandoned which is continuation of Ser. No.07/167,060, filedMar. 11, 1988, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to coreactive photoinitiators forphotopolymerization of systems containing ethylenically unsaturatedcompounds.

Photochemically induced polymerization reactions have taken on greatimportance in industry, in particular when rapid hardening of thinlayers is important, such as, for example, on hardening of paint andresin coatings on paper, metal and plastic, or on drying of printinginks, since these processes are distinguished compared to conventionalmethods of printing and coating objects through a saving in rawmaterials and energy and less environmental pollution. However, thepreparation of polymer materials per se through polymerization ofappropriate unsaturated monomeric star ting materials is also frequentlycarried out photochemically, it being possible to use conventionalprocesses such as solution and emulsion polymerization.

Since, in the reactions mentioned, none of the reactants is generallycap able of absorbing the photochemically active radiation to anadequate extent, it necessary to add so-called photoinitiators which arecapable of either absorbing incident high-energy radiation, usually UVlight, to form active starter radicals, which themselves initiate thephotopolymerization, or of transferring the absorbed energy to one ofthe polymerizable reactants for free-radical formation. The initiatorsdo not normally participate in the actual potymerization reaction.

The major initiators which have hitherto been employed forphotopolymerization of unsaturated compounds are benzophenonederivatives, benzoin ethers, benzil ketals, dibenzosuberone derivatives,anthraquinones, xanthones, thioxanthones, α-haloacetophenonederivatives, dialkoxyacetophenones and hydroxyalkylphenones.

As is known, however, the industrial applicability of many of thesubstances mentioned is limited, in some cases considerably, by a numberof disadvantages. These include, in particular, a frequentlyunsatisfactory reactivity in the ability to initiate photopolymerizationof ethylenically unsaturated compounds. Besides molecule-specificreactivity, the solubility or the ability of the photoinitiators to beincorporated as homogeneously as possible into the photopolymerizablesystems frequently plays a crucial role here.

Further problems are the dark-storage stability of the systems to whichphotoinitiators have been added and the possible influencing of thefinal product by radicals or degradation products of the photoinitiator.Such radicals can lead to a more or less pronounced effect on theproduct's properties, depending on the nature and quantity. Inphotopolymerized paint coatings, the major area of application forphotoinitiators, for example, such radicals can affect the finalachievable hardness of the coating; in addition, undesired colorchanges, for example yellowing, can occur, often only after a relativelylong time. Initiator radicals or degradation products thereof can becomenoticeable due to an unpleasant odour as a consequence of their more orless pronounced volatility; their diffusion from the coating into thesurrounding media can cause problems, for example in packaging materialswhich are provided with photopolymerized coatings, such as, for example,cans and tubes for foods. It is precisely in this area of applicationthat the question of applicability is definitively determined by thepossible or proven toxicity of the photoinitiators and tile degradationproducts thereof.

A particular problem, above all with respect to broad application ofphotoinitiators, is that they can, naturally, only be employed insystems which essentially contain components having olefinic doublebonds which can be polymerized by means of free radicals.

Thermocurable systems based exclusively on polyaddition orpolycondensation reactions which are not induced by free radicals cannotbe converted into radiation-curable systems by adding freeradical-forming photoinitiators. Accordingly, the choice of materialsfor components for radiation-curable systems is limited. Manymaterial-specific properties of thermocurable systems cannot or cannotyet be used in radiation-curable systems without further action. Onealternative here is provided by so-called hybrid binder systems, inwhich thermocurable and photochemically curable components are combinedand in which the thermal and photochemical reactions can take placesimultaneously or successively. However, compatibility problems, inparticular with respect to the photoinitiators to be employed frequentlyarise during development of such systems. Thus there continued to be aparticular demand among experts for photoinitiators which, besidesexcellent initiator properties and good dark storage stability of thesystems to which they have been added, also have a broad applicability,even in systems with a complex composition, and which can themselves, ortheir photolysis products, be bound in such systems in amigration-resistant manner.

Individual steps in this direction have already been taken. Thus, forexample, German Offenlegungsschrift 3,534,645 and EuropeanOffenlegungsschrift 161,463 describe photoinitiators of thehydroxyalkylphenone type which carry specifically olefinicallyunsaturated substituents. These initiators or their photolysis productscan be bound into the polymer composition by copolymerization with thecomponents of the radiation-curable system. They can alternativelyinitially be thermally polymerized themselves and then, as polymeric andas migration-resistant photoinitiators, introduced into theradiation-curable system. However, these specific copolymerizable orpolymeric photoinitiators have an only limited range of applications.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide photoinitiatorswhich are structured so that, besides the ability to initiatepolymerization of ethylenically unsaturated compounds by means of theaction of radiation, they also have the property of reacting with anydesired components of radiation-curable systems, irrespective of whetherthese participate in the photopolymerization reaction or not, whilestill retaining the ability to be stably bound into the resultantpolymer composition.

Upon further study of the specification and appended claims, furtherobjects and advantages of this invention will become apparent to thoseskilled in the art.

It has been found that these objects can be achieved in an excellentfashion by compounds of the formula

    RG--A--IN                                                  (I)

in which

IN is a photoinitiator basic structure ##STR1## wherein R is ##STR2##and R¹ is H, Cl-12-alkyl, halogen or the RG--A--group, or two R¹radicals in the ortho position to the carbonyl group together arealternatively --S--, R² is H, halogen, C₁₋₁₂ -alkyl or C₁₋₁₂ -alkoxy orthe RG--A--group,

R³, R⁴ in each case independent of one another are H, C₁₋₁₂ -alkyl,C₁₋₁₂ -alkenyl, C₁₋₁₂ -alkoxy

R⁵ is OR⁷, N(R⁷)₂, ##STR3## or SO₂ R⁷, R⁶ is C₁₋₆ -alkyl, C₁₋₆-alkanoyl, phenyl benzoyl, each of which is optionally substituted byhalogen, C₁₋₆ -alkyl or C₁₋₆ -alkoxy,

R⁷ is H, C₁₋₆ -alkyl or C₁₋₆ -alkanoyl,

A is a spacer group Z[(CH₂)_(o) Y]_(n) -[(CH₂)_(m) X]₁

wherein

X, Y and Z, in each case independently of one

another, are a single bond, --O--, --S--, --NH--, --CO--, --COO--,--CONH--, --O--CO--, --NH--, --CO--, --COO--, --CONH--, --O--CO--,--NH--CO--or --NH--COO--,

l and m are the numbers 1 to 4,

n and o are the numbers 0 to 4,

RG is one of the functional reactive groups HO--, HS--, H₂ N--, halogen,HO--CO--, H₂ N--CO--, O═C═N--, S═C═N--, N₃ --, SO₂ CL, R^(c) R^(b)C═CR^(a) --

R^(a), R^(b) and R^(c) are in each case independently of one another Hor CH₃,

and with the proviso that Z is not --COO--when n is O and

R⁵ is OR⁷ , or

RG is halogen, cyclopropyl, oxiranly, O═C═N═--R^(d), ##STR4## R^(d) isC₁₋₆ -alkylene or phenylene, and R^(e) is halogen, C₁₋₁₂ -alkyl, C₁₋₁₂-alkoxy or C₁₋₁₂ -alkanoyloxy.

DETAILED DISCUSSION

Some of the compounds of formula I are new. The compounds of formula Iare highly reactive photoinitiators which, irrespective of theirphotoreactivity, can enter into non-photochemically induced(co)reactions and are therefore to be called coreactive photoinitiators.

In the context of the invention, coreactions are to be understood as allreactions which the photoinitiators or photolysis products thereof enterinto with components of radiation-curable systems, with themselves oralternatively with the substrate to which these or an appropriateradiation-curable system is applied as a paint or coating, and whichcause fixed-location bonding of the photoinitiators or the degradationproducts thereof. These coreactions are primarily reactions in whichcovalent chemical bonds are made. However, reactions are also possiblein which the fixing action is based on other interactions, such as, forexample, ionic or polar interactions.

The particular advantage of the compounds according to the inventionover conventional photoinitiators arises from the presence of thereactive RG group, which is linked in the spacer group A and which, inaddition to specific photoreactivity, gives these compounds theopportunity of undergoing non-photochemical reactions. The variety ofreactive groups allows custom matching to a very wide variety ofapplications. The coreaction can take place, independently of the actualphotoreaction before, during or atter the latter. The custom matchingcan be affected by those of ordinary skill using fully conventionalconsiderations, perhaps with a few routine optimization experiments.

Surprisingly, this leads to an unexpectedly large extent ofincorporation of the unreacted photoinitiators or photoinitiatordegradation products into the polymer product which is finally obtained.This very effectively allows undesired influences on the properties ofthe final product to be reduced or entirely eliminated.

In addition, fixing of photoinitiators directly to tile substrate or inthe form of a coating of oligomeric, polymeric or copolymerizedphotoinitiators offers better anchoring of photopolymerizable coatingsapplied to the latter to the substrate or better coating hardening dueto initiator concentrations which are particularly high locally. In thisapplication, in particular, interesting effects and new properties canbe achieved.

Many compounds of the formula I are, in addition, valuable synthesisintermediates on the route to further functionalized photoinitiators orradiation-reactive systems having a covalently bound photoinitiator.

The invention thus relates to the use of the compounds of the formula Ias coreactive photoinitiators for photopolymerization of systemscontaining ethylenically unsaturated compounds, in particular in theradiation curing of coatings having UV-curable paint and binder systems,above all also hybrid binder systems.

The invention also relates to those compounds of formula I per se whichare novel.

The invention furthermore relates to a process for photopolymerizationof systems containing ethylenically unsaturated compounds, at least onecompound of the formula I being added as a coreactive photoinitiator tothe mixture before initiation of the photopolymerization.

In addition, the invention relates to photopolymerizable systemscontaining at least one ethylenically unsaturated, photopolymerizablecompound and, if appropriate, further known and conventional additives,the systems containing at least one compound of the formula I as acoreactive photoinitiator.

Finally, the invention relates to the use of compounds of the formula Ias synthesis intermediates in the preparation of further-functionalizedphotoinitiators and of radiation-reactive systems having a covalentlybound photoinitiator.

The compounds of the formula I are structurally derived from knownphotoinitiators. In the formula I, IN is any photoinitiator structure,which is linked to a functional reactive group RG via a spacer group A,which can, in principle, likewise be any spacer group.

In the compounds of the formula I, photoinitiator properties ofstructural part IN are thus combined with the non-photochemicallyinduced reactivity i.e. coreactivity, of structural part RG.

IN is essentially the aromatic ketone structural unit ##STR5## as ispresent in virtually all classical photoinitiators, but canalternatively be any other structures having photoinitiator properties.

If, in the aromatic ketone structural unit R is an optionallysubstituted phenyl ring, the result is photoinitiators of thebenzophenone series. If, in this case, two R¹ radicals which are orthoto the carbonyl group together form a sulfur bridge between the phenylrings, the result is thioxanthone photoinitiators. Coreactivethioxanthone derivatives are particularly preferred photoinitiators inthe context of the invention.

If R is the --CR³ R⁴ R⁵ group, with the abovementioned definitions forR³ , R⁴ and R⁵, the result is the photoinitiator basic structures ofbenzoin and acyloin ethers, benzil ketals and dialkoxyacetophenones,hydroxyalkylphenones and aminoalkylphenones, and α-sulfonylketones.

Coreactive hydroxyalkylphenone derivatives are likewise particularlypreferred photoinitiators in the context of the invention.

If R is the ##STR6## group, the resulting photoinitiators initiatorsbelong to the class of the acylphosphine oxides.

The spacer group A linking the photoinitiator basic structure IN to thereactive functional group RG preferably has the structure Z[(CH₂)_(o)Y]_(n) -[(CH₂)_(m) X]_(l).

In the simplest case, when X, Y and Z are each a single bond, the spacergroup is an alkylene bridge, preferably having 1 to 8 carbon atoms. Suchan alkylene group can also be linked to the aromatic ring of thephotoinitiator basic structure via a heteroatom when X is --O--, --S--or --NH--.

However, the alkylene bridge may also be interrupted by one or moreheteroatoms, which is the case when Y is --O--, --S-- or --NH--.Interruptions of the alkylene bridge by carbonyl, carboxyl, carboxamideor urethane groups are also possible. Thus, for example, one or moreoxy-, thio or aminoalkylene groups, preferably oxyethyene andthioethylene can function as spacers. Mixed heteroalkylene bridges, inparticular those containing oxygen and sulfur as heteroatoms arelikewise possible. Depending on the chemical nature of the functionalreactive group RG, the Latter is Linked to the spacer group inaccordance with the definitions where Z is a single bond, --O--, --S--,--NH-- or a carboxyl group or a derivative thereof such as a carboxamideor urethane group.

Suitable reactive groups RG are all functional groups which are easilyable to enter non-photochemically induced reactions. The aim of eachsuch reaction is to bind the photoinitiator or photolysis productsthereof into the system at a fixed location. Such reactions can be, forexample, nucleophilic substitutions by or conversely on the RG groupsuch as, for example, esterification, etherification or amidation.Besides halogen, such as, in particular, chlorine and bromine suitableRG groups are, above all, hydroxyl, thiol, carboxyl and sulfonyl groupsand the equivalents thereof. Since, apart from halogens, thesefunctional groups contain acidic H atoms, they are also able to reactwith isocyanate groups from the system to form urethanes or urethaneanalogues. Conversely, the isocyanate group is in turn a particularlypreferred RG group since it can very easily be re acted with componentsof the system which contain functional groups having acidic H atoms.

Preferred reactive RG groups are likewise those which are able toundergo thermally initiated free-radical or ionic polymerization,polyaddition or polycondensation reactions. These include the vinylgroup and the mono- or potymethylated analogues thereof, and thecyclopropyl and oxiranyl groups. Isocyanate-functionalized C₁₋₆ -alkylgroups or phenyl groups are examples of groups which are capable ofpolyaddition. Insertion reactions into any desired components of thesystem can be accomplished by generating carbenes or free radicals, forexample by means of the azide group as the reactive RG group. Forcovalent bonding, the typical reactions of the diazonium group are alsosuitable. Besides polysiloxane formation, the silyl group offers, inparticular, the possibility of covalent linking to the substrate,especially when the latter is of an inorganic nature such as, forexample, glass, ceramic or metal. In accordance with the definitionsgiven for the photoinitiator basic structure IN, the spacer A and thereactive RG group, numerous coreactive photoinitiators having propertieswhich are customized for a very wide variety of applications andpurposes can be achieved through combination.

The compounds of the general formula I can be prepared by standardmethods of organic chemistry. The reactions conditions here can be takenfrom standard works on preparative organic chemistry, for example,HOUBEN-WEYL, Methoden der organischen Chemie, [Methods of OrganicChemistry] , Georg-Thieme Verlag, Stuttgart, or ORGANIC SYNTHESIS, J.Wiley, N.Y., London, Sydney.

It is generally favourable to prepare the photoinitiators according tothe invention, or the precursors thereof, by proven synthetic methods,as are common for the known photoinitiators.

In this preparation it is advantageous to proceed directly from theknown photoinitiators as starting materials and to link the spacer groupA and the reactive group RG to these in one or more steps using commonreactions, such as substitution reactions. However, precursors of knownphotoinitiators which are already suitably substituted can also be usedand the actual photoinitiator active structure be generated in theseonly when the spacer and reactive groups are already present.

The compounds of the general formula I can be used according to theinvention as photoinitiators for photopolymerization of ethylenicallyunsaturated compounds or for curing photopolymerizable systems whichcontain such compounds, and, in particular, also as UV hardeners forpaint coatings, UV-curable binder and hybrid binder systems, printinginks and in radiation curing of aqueous prepolymer dispersions. This usetakes place in a conventional fashion. The compounds to be usedaccording to the invention are generally added to the systems to bepolymerized in amounts from 0.1 to 20% by weight, preferably 0.5 to 12%by weight based on the weight of the entire system.

This addition generally takes place by simple dissolving and stirring insince most of the photoinitiators to be used according to the inventionare liquid or at least readily soluble in the systems to be polymerized.A system to be polymerized is taken to mean a mixture of mono- orpolyfunctional ethylenically unsaturated monomers, oligomers,prepolymers, or polymers, or mixtures of these oligomers, prepolymersand polymers with unsaturated monomers, which can be initiated by freeradicals, it being possible for the mixture to contain, if necessary ordesired, further additives, such as, for example, antioxidants, lightstabilizers, colorants and pigments, but also further knownphotoinitiators and reaction accelerators. Suitable unsaturatedcompounds are all those whose C═C double bonds are activated by, forexample, halogen atoms, carbonyl, cyano, carboxyl, ester, amide, etheror aryl groups or by conjugated further double or triple bonds. Examplesof such compounds are vinyl chloride, vinylidene chloride,acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, methyl,ethyl, n- or tert. butyl, cyclohexyl, 2-ethythexyl, benzyl,phenoxyethyl, hydroxyethyl, hydroxypropyl, lower alkoxy ethyl, andtetrahydrofurfuryl acrylate or methacrylate, vinyl acetate, propionate,acrylate and succinate, N-vinyl pyrrolidone, N-vinylcarbazole styrene,divinylbenzene, substituted styrenes and mixtures of unsaturatedcompounds of these types. Polyunsaturated compounds, such as, forexample, ethylene diacrylate, 1,6-hexanediol diacrylate, propoxylatedbisphenol A diacrylate and dimethacrylate, trimethylolpropane diacrylateand pentaerythritol triacrylate, can also be polymerized with thephotoinitiators used according to the invention. Suitablephotopolymerizable compounds are, in addition, unsaturated oligomers,prepolymers or polymers, and mixtures thereof, with unsaturatedmonomers. These include, for example, unsaturated polyesters,unsaturated acrylic materials, epoxy materials, urethanes, silicones,aminopolyamide resins and, particularly, acrylated resins, such asacrylated silicone oil, acrylated polyesters, acrylated urethanes,acrylated polyamides, acrylated soybean oil, acrylated epoxy resin andacrylated acrylic resin, expediently in a mixture with one or moreacrylates of a mono-, di- or polyalcohol.

The photopolymerizable compounds or systems can be stabilized withoutthereby appreciably impairing the initiator action of thephotoinitiators according to the invention by adding known thermalinhibitors and antioxidants such as, for example, hydroquinone orhydroquinone derivatives, pyrogallol, thiophenols, nitro compounds,β-naphthylamines or β-naphthols, in conventional amounts. Such additionsare intended, above all, to prevent premature polymerization duringproduction of the systems through mixing of the components.

In addition, small amounts of light stabilizers such as, for example,benzophenone derivatives, benzotriazole derivatives,tetraalkylpiperidines or phenyl salicylates, can be added.

In order to exclude the inhibiting action of atmospheric oxygen,paraffin or similar waxy substances are frequently also added tophotopolymerizable systems. As a consequence of poor solubility inpolymers, these float at the beginning of the polymerization and form atransparent surface layer which prevents entry of air. It is alsopossible to deactivate the atmospheric oxygen, for example byintroducing autooxidizable groups, such as, for example allyl groups,into the system to be cured.

The photoinitiators according to the invention can also be used incombination with known free-radical initiators such as, for example,peroxides, hydroperoxides, ketone peroxides or percarboxylates. Inaddition, they can contain pigments or dyes, as are customary, forexample, in photochemically curing printing inks. In this case, theamount of photoinitiator is chosen to be higher, for example 6 to 12% byweight, whereas 0.1 to 5% by weight are fully sufficient in most casesfor colorless photopolymerizable products. Depending on the intendedapplication, fillers, such as talc, gypsum or silica, fibers, organicadditives, such as thixotropic agents, levelling agents, binders,lubricants, flatting agents, plasticizers, wetting agents, silicones forimproving the surface quality, antifloating agents or minor amounts ofsolvents can be added.

Suitable known photoinitiators which can be used, if appropriate,together with the initiators according to the invention, are, forexample, benzophenones, such as, for example, Michler's ketone[4,4'-bis(dimethylamino)-benzophenone],4,4'-bis(diethylamino)benzophenone, p-dimethylaminobenzophenone,p-chlorobenzophenone and benzophenone; anthraquinones, such as, forexample, anthraquinone, 2-chloroanthraquinone and 2-alkylanthraquinones;xanthones, such as, for example 2-haloxanthones or 2-alkylxanthones;thioxanthones, such as 2-chlorothioxanthone and 2-alkylthioxanthones;acridanones, such as, for example, 2-alkylacridanones or N-substitutedacridanones; benzoins, such as, for example, p-dimethylaminobenzoin andalkyl ethers of benzoin; benzil ketals, α-haloketones,dialkoxyacetophenones, α-hydroxyalkylphenones and α-aminoalkylphenones,as described, for example, in German Offenlegungsschrift 2,722,264 andEuropean Offenlegungsschrift 3,002, and furthermore, for example,fluorenones, dibenzosuberones, phenanthrenequinones and benzoates, suchas, for example, hydroxypropyl benzoate and benzoyl benzoate acrylate.Mixtures with known initiators generally contain the coreactivephotoinitiators to be used according to the invention in proportions ofat least 10% by weight, advantageously from 50 to 95% by weight relativeto the total amount of the initiator mixture employed.

Besides the photoinitiators according to the invention, it isadvantageous to employ reaction accelerators in the photopolymerizablesystems. Examples of such compounds which can be added are organicamines, phosphines, alcohols and/or thiols all of which have at leastone CH group in the α position to the heteroatom. For example, primary,secondary and tertiary aliphatic, aromatic, araliphatic or heterocyclicamines, as described, for example, in U.S. Pat. No. 3,759,807, aresuitable. Examples of such amines are butylamine, dibutylamine,tributylamine, cyclohexylamine, benzyldimethylamine, dicyclohexylamine,triethanolamine, N-methyldiethanolamine, phenyldiethanolamine,piperidine, piperazine, morpholine, pyridine, quinoline, ethylp-dimethylaminobenzoate, butyl p-dimethylamino benzoate,4,4'-bis(dimethylamino)-benzophenone (Michler's ketone) or4,4'-bis(diethylamino)-benzophenone. Particular preference is given totertiary amines such as, for example, trimethylamine, triisopropylaminetributyla mine, octyldimethylamine, dodecyldimethylamine, triethanolamine, N-methyldiethanolamine, N-butyldiethanolamine,tris(hydroxypropyl)amine, and alkyl dimethylamino benzoate. Furtherexamples of suitable reaction accelerators are trialkyl phosphines,secondary alcohols and thiols. The addition of reaction accelerators ofthese types can take place in amounts which are conventional for them.

Photopolymerizable systems which additionally contain a tertiary organicamine as reaction accelerator represent a particularly preferred form ofthe present invention.

The term "photopolymerization of ethylenically unsaturated compounds"should be understood in the broadest sense. It also includes, forexample, further polymerization or crosslinking of polymeric materials,such as prepolymers, the homo-, co- and terpolymerization of simplemonomers and also the combination of the types of reaction mentioned.

The photopolymerization can be initiated through the action ofhigh-energy irradiation, preferably UV light, on the photopolymerizablesystems, containing coreactive photoinitiators according to theinvention. The photopolymerization takes place by methods which areknown per se, through irradiation with light or UV irradiation in thewavelength range from 250 to 500 nm, preferably 300-400 nm. Irradiationsources which may be used are sunlight or artificial-light lamps.Mercury high-pressure, medium-pressure or low-pressure lamps and xenonand tungsten lamps, for example, are advantageous.

The photopolymerization using the photoinitiators according to theinvention can be carried out either batchwise or continuously. Theduration of irradiation depends on the way in which thephotopolymerization is carried out, on the type and quantity ofpolymerizable materials employed, on the type and concentration ofphotoinitiators used, and on the intensity of the light source and canbe in the range from several seconds to minutes, such as, for example,on irradiation curing of coatings, but may also be in the hours regionin the case of large batches such as, for example, in bulkpolymerization.

The compounds of the formula I according to the invention are preferablyused as photoinitiators in UV curing of thin coatings such as, forexample, paint coatings, on all materials and substrates which areconventional for this. These can primarily be paper, wood, textilesubstrates, plastic and metal. An important area of application is alsothe drying or hardening of printing inks and screen printing materials,of which the latter are preferably employed in surface coating orshaping of, for example, cans, tubes and metal sealing caps. As aconsequence of the substantial to complete absence of free initiatorradicals after photopolymerization has taken place in systems to whichcoreactive photoinitiators according to the invention have been added,the systems are particularly suitable in areas of application wherediffusion of such radicals into media surrounding the correspondingfinal products is to be excluded, for example when packaging which isprovided with photopolymerized coatings comes into contact withfoodstuffs.

The essential classes of the coreactive photoinitiators according to theinvention, typical representatives and the preparation and preferredmanner of use thereof are shown below.

Compounds of the subformula II ##STR7## having the abovementionedmeanings for the particular substituents essentially represent theparticularly preferred coreactive photoinitiators of thehydroxyalkylphenone type (R³ and R⁴ are C₁₋₁₂ -alkyl, R⁵ is OH) and theamino alkylphenone type (R⁵ is, if appropriate, also alkylsubstitutedamino), and in addition coreactive derivatives of benzoin ethers (R³ isphenyl, R⁴ is H, C₁₋₁₂ -alkyl or phenyl, R⁵ is C₁₋₁₂ -alkoxy), benzilketals (R³ is phenyl, R⁴ and R⁵ are C₁₋₁₂ alkoxy) anddialkoxyacetophenones (R³ is H, C₁₋₁₂ -alkyl, R⁴ and R⁵ are C₁₋₁₂-alkoxy).

Besides the functionalization of conventional photoinitiators which arecommercially available or can be prepared by known methods, particularimportance is attached in the preparation of compounds of the formulaII, in particular in the preferred hydroxyalkylphenone andaminoalkylphenone derivatives, to the preparation from appropriatelysubstituted precursors on which the photoinitiators are based, ananalogous procedure to methods which are known for this purpose beingfollowed. These methods are described in detail, for example, in GermanOffenlegungsschrift 2,722,264 and European Offenlegungsschrift 3,002.Coreactive hydroxyalkylphenone derivatives can be obtained, for examplefrom suitable phenyl derivatives which already contain the spacer groupA and the functional group RG or appropriate precursors, by carrying outa Friedel-Crafts acylation using an appropriate acyl halide in order tointroduce the active photoinitiator structure or a precursor thereof.Phenyl derivatives which can be employed as suitable starting materialsare, for example, phenol, phenyl thiol, phenoxyacetic acid and monooorpolyethoxylated phenol, such as 2-hydroxyethyl phenyl ether. For theFriedel-Crafts acylation, it is advisable in some cases to protect theterminal functional groups by suitable protecting groups which can beremoved later, such as by acylation in the case of the OH group. Anilinederivatives can be acylated under Vilsmeier conditions, for exampleusing N,N-dimethylisobutyramide and phosphorus oxychloride.

In order to produce the active photoinitiator structure of thehydroxyalkyl phenone type, an acylation can be carried out, for example,using isobutyryl halide or α-chloroisobutyryl halide and subsequentlyintroducing the hydroxyl, alkoxy or alkanoyloxy group. Thus, forexample, Friedel-Crafts acylation of acylated 2-hydroxyethyl phenylether using isobutyryl chloride and subsequent bromination andhydrolysis on the tertiary carbon atom leads to the compound4-(2-hydroxyethoxy)phenyl 2-hydroxy-2-propyl ketone. ##STR8##

The compound IIa, which has already been described per se and as aphotoinitiator for aqueous systems in German Offenlegungsschrift3,512,179 is of central importance here since, due to the terminal OHgroup, it is capable, on the one hand, of coreactivity in the sense ofthe invention, but, on the other hand, can also serve as an intermediatefor a large number of further coreactive photoinitiators which arederived from this and which contain other functional groups.

This compound is also especially suitable as a coreactive photoinitiatorin hybrid binder systems. Such systems very generally contain at leastone thermocuring component and one photochemically curing component. Thethermocuring component is normally a two or multicomponent reactionresin, preferably of the polyol/polyisocyanate type. Suitablephotochemically curing components are all monomeric, oligomeric orpolymeric unsaturated compounds which are conventional for this purpose,and combinations thereof, whose polymerization or crosslinking takesplace through the influence of high-energy irradiation and with the aidof the photoinitiator. Such hybrid systems can be obtained by mixing allthe components, the isocyanate component, as usual forpolyurethane-forming reactive resins, expediently not being added untiljust before use in order to prevent premature curing of thethermopolymerizing component. Coatings produced using such hybridsystems are cured by initially irradiating them in a fashion which isconventional for radiation-curing systems, rapid surface drying andcuring of the coating being achieved. The fully cured state is reachedafter completion of the thermal reaction, which can also be acceleratedby applying heat. The advantage of these systems over slow-dryingsystems on a purely thermal reactive resin basis is the considerablesaving in time and energy; the coated articles can be stackedimmediately or further processed more quickly.

The advantage of the coreactive photoinitiators according to theinvention, such as compound IIa, on use in hybrid binder systems isthat, in contrast to conventional photoinitiators, virtually nophotoinitiator residues or photolysis products thereof can be detectedin the fully cured polymer material, as shown by extraction experiments.Accordingly, the polymer products exhibit a relatively high finalhardness. Adverse effects due to the initiator such as, for example,odor or yellowing, are not observed. Due to the coreactive OH group, thephotoinitiator according to the invention is incorporated covalentlyinto the polymer material through reaction with equivalent amounts ofthe isocyanate component of the thermally curing component in the hybridbinder system.

Compound IIa can also be fixed covalently in both purelyradiation-curable systems and in hybrid systems through esterificationby means of carboxylic acid group-containing components. Examples ofsuch components are, for example, terephthalic acid, pyromellitic acidand anhydrides thereof, and oligomers or polymers which are derived fromthese compounds and contain at least one free carboxylic acid function.

Coreactive photoinitiators according to the invention which are derivedfrom compound IIa are, for example:

4-[2-(oxiranylmethoxy)ethoxy]phenyl 2-hydroxy-2-propyl ketone ##STR9##4-(2-allyloxyethoxy)phenyl 2-hydroxy-2-propyl ketone ##STR10##4-[2-(3-triethoxysilylpropoxy)ethoxy] phenyl 2-hydroxy-2-propyl ketone##STR11## 4-(2-aminoethoxy)phenyl 2-hydroxy-2-propyl ketone ##STR12##4-(2-azidoethoxy)phenyl 2-hydroxy-2-propyl ketone ##STR13##

The compounds IIb and IIc can be obtained from IIathrough reaction withepichlorohydrin or allyl bromide. Compound IId d can be obtained fromIIc through subsequent reaction with triethoxysilane.

Compound IIe can be prepared, for example, by hydrogenation of IIf.

Compound IIf is obtained by reacting the ptoluenesulfonate of IIa withsodium azide.

The epoxy-functionalized photoinitiator IIb can advantageously beemployed, in particular, in hybrid binder systems whose thermocurablecomponent is a reactive resin of the epoxy type. Due to the epoxyfunction, IIb or its photolysis products are bound virtually completelyinto the epoxy polymer of the binder system.

The photoinitiator IIc which is functionalized with an unsaturatedcomponent can be copolymerized with unsaturated components of anyradiation-curable compositions. It can also be thermally polymerizeditself. The resultant polymeric photoinitiator can be added toradiation-curable compositions, where it remains migration-resistant,due to its polymeric character. It can also be initially applied only asa polymeric initiator coating to a substrate. A photocurable paintcoating which is applied on top and which does not require any furtheraddition of initiator can then be cured with excellent substrateadhesion.

The silyl-functionalized initiator IId can be employed in an analogousfashion, its use bringing advantages primarily in the coating ofinorganic substrates such as metals, glass or other silicate materials,due to the adhesion-improving silyl groups.

Compound IIe can be employed analogously to IIa; compound IIf is highlyreactive due to the azido group and is capable, for example, ofinsertion reactions.

The carboxylic acid-functionalized photoinitiator4-(hydroxycarbonylmethoxy)phenyl 2-hydroxy-2-propyl ketone ##STR14##allows fixing by reactions which are typical of carboxylic acids such assalt formation, esterification, acid amide formation etc. Fixing byesterification with macromolecular polyhydroxyl compounds, such ascellulose and related materials is particularly important.

In materials which have been modified in this fashion, a very highinitiator concentration is achieved at the surface which is veryadvantageous for subsequent further modification usingphotopolymerizable materials, such as in photoinitiated grafting ofmonomers ("photografting").

The following coreactive photoinitiators can be

prepared in an analogous fashion and can be used like the abovementionedcompounds:

4-allyloxyphenyl 2-hydroxy-2-propyl ketone ##STR15##4-oxiranylmethoxyphenyl 2-hydroxy-2-propyl ketone ##STR16##4-[3-(triethoxysilyl)propoxy]phenyl 2-hydroxy-2-propyl ketone ##STR17##4-[2-(3-triethoxysilylpropylthio)ethyl]phenyl 2-hydroxy-2propyl ketone##STR18## 4-(2-chloroethoxy)phenyl 2-hydroxy-2-propyl ketone ##STR19##4-(oxiranylmethoxycarbonylmethoxy)phenyl 2-hydroxy-2-propyl ketone##STR20## 4-oxiranylmethoxyphenyl α-isopropoxybenzyl ketone ##STR21##4-[3-(triethoxysilyl)propoxy]pheny α-isopropoxybenzyl ketone ##STR22##4-oxiranylmethoxyphenyl α,α-dimethoxybenzyl ketone ##STR23##4-[3-(triethoxysiyl)propoxy]phenyl α,α-dimethoxybenzyl ketone ##STR24##4-(2-isocyanatoethoxy)phenyl 2-hydroxy-2-propyl ketone ##STR25##4-(2-isothiocyanatoethoxy)phenyl 2-hydroxy-2-propyl ketone ##STR26##4-(2-hydroxy-2-methylpropionyl)phenoxyacetamide ##STR27##4-(2-hydroxy-2-methylpropionyl )phenoxyacetohydrazide ##STR28##N-[4-(2-hydroxy-2-methylpropionyl)phenoxyacetyl]-hydroxylamine ##STR29##N-[4-(2-hydroxy-2-methylpropionyl)phenoxyacetyl]-N'-acryloylhydrazine##STR30## 4-isocyanatomethoxyphenyl 2-hydroxy-2-propyl ketone ##STR31##vinyl 4-(2-hydroxy-2-metbylpropionyl )phenoxyacetate ##STR32## Compoundsof the subformula III ##STR33## having the abovementioned meanings forthe respective substituents represent the likewise particularlypreferred coreactive photoinitiators of the thioxanthone type.

Starting materials for these are commercially available thioxanthonephotoinitiators, or derivatives thereof, which are predestined forsimple introduction of the spacer group A and functional groups RG.Particularly suitable such starting materials are 2-chlorothioxanthoneand 2-hydroxythioxanthone.

The hydroxyl-functionalized photoinitiator2-(2-hydroxyethylthio)thioxanthone (IIIa) is obtained by reacting2-chlorothioxanthone with, for example, 2-mercaptoethanol.

The amino-functionalized photoinitiator 2-(2-aminoethylthio)thioxanthone(IIIb) can be obtained in a similar fashion.

Both compounds can be employed entirely analogously to compound IIa ascoreactive photoinitiators, in particular also in hybrid binder systems.

Compounds IIIa and IIIb, Likewise entirely analogously to compounds IIa,can also in turn serve as the starting material for further coreactivephotoinitiators having other functional groups. Thus, thephotoinitiators 2-[2-(acryloyloxy)ethylthio]thioxanthone (IIIc)2-[2-(acryloylamino)ethylthio]thioxanthone (IIId)2-[2-(allyloxy)ethylthio]thioxanthone (IIIe) and2-[2-(allylamino)ethylthio]thioxanthone (IIIf) which are functionalizedby an unsaturated group can be obtained, for example, through reactionwith acrylyl chloride or allyl bromide.

These compounds are highly suitable as photoinitiators which can becopolymerized with unsaturated components of radiation-curablecompositions. However, they can also be thermally polymerized bythemselves and used as polymeric photoinitiators as described forcompound IIc.

Isocyanate-functionalized photoinitiators, such as, for example2-[2-(6-isocyanatohexylaminocarbonyloxy)ethoxy]thioxanthone ##STR34##can be obtained by reacting IIIa with an equivalent amount of adiisocyanate. Covalent binding into the radiationcurable polymer systemcan take place through reaction of the isocyanate group with OH groupsof the components. Use in hybrid binder systems which contain, asthermocurable component, a polyurethane-forming reactive system isparticularly favourable. The isocyanate-functionalized photoinitiatorcan be mixed h ere with the isocyanate hardener of the reactive resincomponent, and this mixture can be used, as it were, as a "hybridhardener".

In an analogous fashion, as described for the corresponding compounds ofthe subformula II, epoxy-, silyl- and carboxylic acid-functionalizedthioxanthone derivatives can be obtained and correspondingly employed,such as, for example, the compounds 2-(oxiranylmethoxy)thioxanthone(IIIh) and 2-[3-(triethoxysilyl)propoxy]thioxanthone (IIIi).

The coreactive photoinitiators of this invention are preferably added tothe mixture to be polymerized prior to initiation of thephotopolymerization reaction.

This invention preferably is applied to non-aqueous systems, e.g.,polymerizable compositions containing no more than about 10% of water.

Further details regarding the structures of the photoinitiatorcomponent, the polymerizable monomers and prepolymers, the curableprepolymers, polymeric oligomers and the thermocurable components, aswell as other conventional aspects of the use of photoinitiators areknown and disclosed in, e.g., German Offenlegungsschrift 2,722,264 (U.S.Pat. No. 4,347,111), European Offenlegungschrift 3,002 (U.S. Pat. No.4,308,400) and the other references cited above

Without further elaboration, it is believed that one skilled in the artcan, using the preceding description; utilize the present invention toits fullest extent. The following preferred specific embodiments are,therefore, to be construed as merely illustrative, and not limitative ofthe remainder of the disclosure in any way whatsoever.

In the foregoing and in the following examples, all temperatures are setforth uncorrected in degrees Celsius and unless otherwise indicated, allparts and percentages are by weight.

The entire text of all applications, patents and publications, if any,cited above and below are hereby incorporated by reference.

EXAMPLE 1

4-(2-Hydroxyethoxy)phenyl 2-hydroxy-2-propyl ketone (IIa)

a) 336 g (3.2 mol) of isobutyryl chloride are added dropwise over thecourse of 40 minutes while stirring to 880 g. (8.8 mol) of anhydrousaluminium chloride in 480 ml of dichloromethane at -5 to 0° C. 540 g.(3.0 mol) of 2-phenoxyethyl acetate are then added dropwise over thecourse of 2 hours at the same temperature. The reaction mixture isstirred for a further 2 hours at the stated temperature and then pouredinto a mixture of 1.8 l of concentrated hydrochloric acid and 5 kg ofice. The organic phase is separated off and the aqueous layer isextracted with dichloromethane. The combined organic phases are washedwith water, dried and evaporated, and the residue is distilled in vacuo.740 g. of 4-(2-acetoxyethoxy)phenyl-2-propyl ketone of boiling point145-152° C./0.3-0.5 torr are obtained. b) 205 g. (1.0 mol) of4-(2-acetoxyethoxy)phenyl 2-propyl ketone are dissolved in 200 ml ofglacial acetic acid, and 192 g. (1.2 mol) of bromine are added over thecourse of 2 hours with stirring at 25° C. The mixture is then stirredfor about a further 10 hours and then poured into 3 L of ice water. Theproduct is extracted with ethyl acetate. The combined extracts aredried, and 365 g. of a viscous oil are obtained by evaporation. This oilis dissolved in 1 L of ethanol, and 380 g. of 32% strength sodiumhydroxide solution are added over the course of 20 minutes with stirringat 25° C. The mixture is stirred for a further 10 minutes and theethanol is then removed. The oily residue is transferred into 3 l of icewater, and this mixture is extracted repeatedly with a total of 1.5 l ofethyl acetate. After drying, filtering and evaporating the solution, 250g. of an oily crude product are isolated. Through recrystallization fromacetone/petroleum ether and/or chromatographic purification, 145 g of4-(2-hydroxyethoxy)phenyl 2-hydroxy-2-propyl ketone are obtained in theform of a colourless solid of melting point 88°-90° C.

EXAMPLE 2

4-(2-allyloxyethoxy)phenyl 2-hydroxy-2-propyl ketone (IIc)

26.8 g. (0.22 mol) of allyl bromide and 1.8 g. of methyltrioctylammoniumchloride as phase-transfer catalyst are added to a mixture of 44.9 g.(0.2 mol) of IIa and 8.8 g. (0.22 mol) of granulated sodium hydroxide in300 ml of toluene, and the mixture is stirred for 20 hours at 50° C. Themixture is then extracted with toluene. Conventional work-up andchromatographic purification give 28.5 g. of the analytically purecompound IIc.

EXAMPLE 3

4-[2-(Oxiranylmethoxy)ethoxy]phenyl 2-hydroxy-2-propyl ketone (IIb).

Through reaction analogously to example 2, but using epichlorohydrin,compound IIb is obtained.

EXAMPLE 4

4-[2-(3-Triethoxysilylpropoxy)ethoxy]phenyl 2-hydroxy-2propyl ketone(IId)

5.3 g. (0.02 mol) of compound IIc, 4.9 g. (0.03 mol) of triethoxysilaneand 20 mg of platinum catalyst (norbor-nene-Pt acetylacetonate complex)in 50 ml of methylene chloride are refluxed for 4 hours under nitrogen.After evaporation of the mixture and chromatographic purification of theresidue, 3.4 g. of the analytically pure compound IId are obtained.

EXAMPLE 5

4-(hydroxycarbonylmethoxy)phenyl 2-hydroxy-2-propyl ketone (IIg)

612 g. of compound IIg of melting point 131°-134° C. are obtainedanalogously to Example 1 from 931 g. (5.6 mol) of methyl phenoxyacetateby Friedel-Crafts acylation using 657 g. (6.2 mol) of isobutyrylchloride and subsequent bromination and hydrolysis.

EXAMPLE 6

4-(2-Hydroxy-2-methylpropionyl)phenoxyacetamide (IIt)

75.0 g. of 25% strength ammonia are added dropwise with stirring to 25.2g. (0.1 mol) of methyl 4-(2-hydroxy-2-methylpropionyl) phenoxyacetate(obtained by esterifying compound IIg. using methanol) in 50 ml. ofdioxane. After being stirred for 2 hours, the mixture is evaporated tosolidification. The crude product is recrystallized from hot water, 22.1g. of compound IIt of melting point 139° C. being obtained.

EXAMPLE 7

4-(2-Azidoethoxy)phenyl 2-hydroxy-2-propyl ketone (IIf)

37.8 g. (0.1 mol) of 4-(2-p-tolylsulfonyloxyethoxy)-phenyl2-hydroxy-2-propyl ketone (obtained by reacting compound IIa withp-toluenesulfonyl chloride) and 9.8 g. (0.15 mol) of sodium azide arestirred for one hour in 100 ml. of DMSO at 60° C. Through extractivework-up using water and ether or methyl t-butyl ether, 22.4 g. ofcompound IIf are obtained as a pale yellow, readily mobile oil. IR:v=2114 cm. ⁻¹ (N₃).

EXAMPLE 8

4-Allyloxyphenyl 2-hydroxy-2-propyl ketone (IIh)

6.6 g. (0.22 mol) of sodium hydride (80% strength in paraffin oil) areadded in portions to 36.0 g (0.2 mol) of 4-hydroxyphenyl2-hydroxy-2-propyl ketone in 450 ml. of dimethyl sulfoxide under aninert gas and the mixture is stirred for 15 minutes at room temperature.26.8 g. (0.22mol) of allyl bromide in 40 ml. of dimethyl sulfoxide arethen added dropwise at 30°-40° C., and the mixture is stirred for 15minutes. The reaction mixture is poured into 2 l of water and thenextracted with methyl t-butyl ether. By removing the solvent, 41.5 g. ofcompound IIh are obtained.

EXAMPLE 9

4-Oxiranylmethoxyphenyl 2-hydroxy-2-propyl ketone (IIi)

Analogously to Example 3, 6.8 g. of the analytically pure compound IIiof melting point 54° C. are obtained from 36.0 g. (0.2 mol) of4-hydroxyphenyl 2-hydroxy-2-propyl ketone and 19.0 g. (0.2 mol) ofepichlorohydrin.

EXAMPLE 10

4-[3-(Triethoxysilyl)propoxy]-phenyl 2-hydroxy-2-propyl ketone (IIj)

Analogously to Example 4, 10.2 g. of the analytic-ally pure compound IIjare obtained from 14.3 g. (0,065 mol) of IIg and 16.0 g. (0.0975 mol) oftriethoxysilane.

EXAMPLE 11

2-(2-Hydroxyethylthio)thioxanthone (IlIa)

5.6 g. (0.0225 mol) of 2-chlorothioxanthone and 2.6 g. (0.0225 mol) ofthe potassium salt of 2-mercaptoethanol are stirred for 18 hours in 20mol of N,N-dimethylacetamide at 100° C. The reaction mixture is thenpoured into 2N hydrochloric acid and extracted with ethyl acetate. Afterconventional work-up and chromatographic purification, 3.5 g. of theanalytically pure compound IIIaof melting point 94° C. are obtained.

EXAMPLE 12

2-(2-Aminoethylthio)thioxanthone (IIIb)

17.0 g. (0.15 mol) of cysteaminium chloride and 19.8 g. (0.3 mol) ofpotassium hydroxide are boiled for 3 hours on a water separator in 180ml. of toluene. 24.6 g. (0.1 mol) of 2-chlorothioxanthone and 180 mol ofdimethylpropyleneurea are added to the evaporated residue, and themixture is stirred for 20 hours at 100° C. The reaction mixture ispoured into 1 l of 2N hydrochloric acid and the aqueous phase isextracted with ethyl acetate. The aqueous phase then adjusted to pH 10and extracted with ethyl acetate. Work-up of the organic phase gives24.0 g. of the analytically pure compound IIIb.

EXAMPLE 13

2-[2-(acryloyloxy)ethylthio]thioxanthone (IIIc)

6.8 g. (0.075 ml) of acrylyl chloride 30 ml of toluene are addeddropwise with stirring to 14.0 g (0.05 mol) of compound IIIa, 6.0 g ofpyridine and 0.07 g of 4- methoxyphenol in 150 ml. of toluene at roomtemperature. After stirring for 3 hours at 50° C., 500 ml of water and250 ml. of ethyl acetate are added to the mixture. Work-up of theorganic phase and chromatographic purification give 5.0 g of theanalytically pure compound IIIc of melting point 68-20 71° C.

EXAMPLE 14

2-[2-(Acryloylamino)ethylthio]thioxanthone (IIId)

Analogously to Example 10, 4.6 g of the analytically pure compound IIIdof melting point 161° C. are obtained from 14.5 g (0.05 mol) of compoundIIIb and 5.0 g. (0.055 mol) of acrylyl chloride.

EXAMPLE 15

Polymeric photoinitiator

18.6 g (0.05 mol) of 2-[2-(acryloyloxy)ethylthio thioxanthone (IIIe) and0.15 g of dibenzoyl peroxide are refluxed for 20 hours in 100 ml oftoluene. The polymeric product obtained is purified by reprecipitationfrom methylene chloride/n-hexane. A yellow amorphous powder, whoseaverage molecular weight is determined at about 3200 by means ofgel-permeation chromatography, is obtained.

Examples 16-21 below illustrate the use according to the invention ofthe coreactive photoinitiators in radiation curing of photopolymerizablebinder systems.

EXAMPLE 16

Hybrid binder system

A hybrid binder system comprising 40.5 parts by weight of a hydroxylgroup-containing polyacrylate/about 65% strength in butyl acetate/xylene(Desmophen® A 365, Messrs. Bayer AG), 17.0 parts by weight of analiphatic polyisocyanate/about 75% strength in methoxypropylacetate/xylene (Desmodur® N 75, Messrs. Bayer AG), 30.0 parts by weightof an acrylated polyurethane prepolymer (VPS 1748, Messrs. Degussa AG),20.0 parts by weight of hexanediol diacrylate, 7.5 parts by weight ofpentaerythritol triacrylate and 5.0 parts by weight of thehydroxyl-functionalized photoinitiator IIa was prepared by mixing thecomponents, the polyisocyanate not being added until just before use.

The ready-to-use hybrid binder system was applied in a coating thicknessof 50 μm using a spiral hand coater onto glass plates (10×10 cm). Aftera drying time of 5 minutes, the coatings were cured using a UVirradiator (Messrs. Beltron), through which the plates are fed on aconveyor belt at a belt speed between 2.5 and 40 m/min under two Hgmedium-pressure lamps of power 50 watt/cm each at a distance of 10 cm.

At belt speeds between 2.5 and 15 m/min, solid paint coatings with a drysurface were obtained immediately.

Thermal post-curing of the polyurethane reactive resin component gave afinal hardness of the coatings of:

for 20 hours/room temperature: 168 seconds

for 1 hour/60° C.: 188 seconds

for 3 hours/60° C.: 198 seconds (Konig pendulum hardness)

After extraction of fully cured coating material with acetonitrile, theproportion of initiator which is not bound into the material isdetermined by means of high-pressure liquid chromatography at a maximumof 3% of the original amount employed.

In an analogous fashion, equally good results are obtained usinginitiators IIIa and IIIb.

EXAMPLE 17

UV-curable binder system

A UV-curable binder system comprising 60 parts by weight of an acrylatedpolyurethan e prepolymer (prepolymer VSP 1748, Messrs. Degussa AG), 40parts by weight of hexanediol diacrylate, 15 parts by weight ofpentaerythritol triacrylate and 5 parts by weight of the photoinitiatorIIc which is functionalized with unsaturated groups, was processedanalogously to Examples 16 to give 50 μm thick coatings and cured at abelt speed of 10 m/min. The fully cured coatings obtained are entirelyfree of odour and colourless.

In an analogous fashion, equally good results are obtained usinginitiators IIh and IIIc-IIIf.

EXAMPLE 18

UV-curable pigmented binder system

30 parts by weight of titanium dioxide (anatase) were incorporatedhomogene ously into 60 parts by weight of an acrylated epoxy prepolymer(Laromer® PE 55 F, Messrs. BASF AG) and 40 parts by weight of hexanedioldiacrylate. 4 parts by weight of the thioxanthone photoinitiator IIIcwhich is functionalized by unsaturated groups and 8 parts by weight ofN-methyldiethanolamine as coinitiator are subsequently stirred into themixture. It was possible to harden the paint, applied to glass plates ina coating thickness of 12 μm at belt speeds between 2.5 and 20 m/min andan irradiation power of 120 W/cm to give solid coatings having a drysurface.

At a belt speed of 2.5 m/min, pendulum the Konig pendulum hardness is155 seconds. Paint films are odourless and yellowing-free.

EXAMPLE 19

On curing at 2.5 m/min, the corresponding use of thehydroxyl-functionalized thioxanthone photoinitiator IlIa gave paintcoatings having a pendulum hardness of 149 seconds.

EXAMPLE 20

UV-curable binder system

It was possible to cure coatings of thickness 50 μm with a systemcomprising 75 parts by weight of an acrylated epoxy prepolymer (Laromer®EA 81, Messrs. BASF AG) and 25 parts by weight of hexanediol diacrylateat a belt speed of 2.5 m/min and an irradiation power of 80 W/cm withinitiation using 0.5% by weight of the thioxanthone derivative IIIdwhich is functionalized by unsaturated groups and 2.0% by weight ofN-methyldiethanolamine to give paint coatings having a pendulum hardnessof 172 seconds.

EXAMPLE 21

Coating curing using substrate-bound initiator

A 25% strength ethanolic solution of the silyl-functionalizedphotoinitiator IId was whirler coated onto glass plates (5×5 cm), andthe plates thus treated were heated for 30 minutes at 190° C. The plateswere then rinsed with acetone and coated with a mixture of 75 parts byweight of an acrylated epoxy prepolymer (Laromer® EA 81, Messrs. BASFAG) and 25 parts by weight of hexanediol diacrylate. After UV curing at3.75 m/mim and an irradiation power of 120 W/cm and rinsing again withacetone, hard, very strongly adherent coatings of thickness 0.7-0.8 μmwere obtained. Corresponding results are obtained using initiator IIj.

The preceding examples can be repeated with similar success bysubstituting the generically or specifically described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

What is claimed is:
 1. A process for photopolymerizing a radiationcurable system by attaching a photoinitiator of the formula:

    RG--A--IN

in which IN is of the formula ##STR35## , wherein R is CR₃ R₄ R₅, R₃, R₄in each case independently of one another are H,C₁ -C₁₂ alkyl,C_(1-C) ₁₂alkoxy, phenyl or together form C₂ -C₆ alkylene, R₅ is -OR₇, R₇ H or C₁-C₆ alkyl, A is a spacer group Z[(CH₂)_(o) Y]_(n) -[(CH₂)_(m) X]_(l),wherein X is --O--, Y is --O--,--NH--or --O--CO--, Z is a single bond,--NH--, --NHCO--or--CONH--, l is 1 m is an integer from 1 to 4, o is aninteger from 0 to 4, n is 1, if Y is --O--CO-- and n is an integer from0 to 4, if Y is --O-- or --NH--, RG is (R_(e))₃ Si--or N₃ -- and R_(e)is C₁ -C₁₂ alkoxy, directly to a substrate with the reactive group RG byheating, applying at least one ethylenically unsaturated compound andsubjecting said radiation curable system to activating radiation withwavelengths from 250-500 nm.